22' pontoon prop question.

[joegibbstruck]

I know it has probably been covered and recovered a million times, but there is allot of mixed reviews on the subject.

I recently bought a new to me pontoon boat, it's a 2002 22' fisher with a 2002 mercury 125 2 stroke and gear ratio of 2.07 and no lifting strakes or anything like that. Its relatively light, has poly sheeting decking plastic furniture etc... with me and 5 kids on board and trimmed all the way down it reaches max RPM of 5450 and a top speed of 17mph trimmed all the way down and if I start to trim up if will go to 19mph but loses traction really quick( way before the prop even gets close to the surface). It goes from 0-17/19mph in about 10 seconds right now and then bounces on the rev limiter the prop is a quick silver 77342a45(p15) 13.75" x 15p 3 blade aluminum. From all the calculators I have figured it has about 49% prop slip. Which I believe to be pretty high, I know pontoons will have more slip, but I would think closer to 25/30%

My questions are should I go with larger diameter and less pitch for more traction, or more pitch for speed? I know getting the slip lower should help in both cases, but I am trying to figure out which direction to go? I found someone local to me who has a new quicksilver aluminum prop 15" diameter and 17 pitch for $50 but I'm not a fan of wasting money on trial and error. And figured there should be enough knowledge to help me decide while spending the least amount of money lol.

Ultimately, if possible, I would like to be able to cruise around 25-27mph WOT and be able to pull a tube with 2 kids on it occasionally. It's mostly a fishing vessel for the family. Any and all help would be extremely appreciated.

 

[jlh3rd]

what is the diameter of your pontoons? Makes a big difference.

I have a 2006 , 24' pontoon, 25" diameter toons and a 2021 Mercury 115 hp CT, purchased new.
By myself I get 26 mph, 5800+ rpm @WOT. Both a Merc 4-14x14 and a 3-16x13 props give these numbers.
A merc. 3-16x12 prop gets me over 6000 rpm and about 24 mph but I used that prop to pull two tubes with 5 thin teenagers and 4 on board which kept my rpms around 5600+ and about 21+ mph. What I wanted.
When pulling a load, I wanted my motor's rpm in the upper range of the 5000-6000 rpm operating range. ( don't know yours).
Your boat is 2' shorter and 10 more horses. Your performance should be better than mine, unless your toons are smaller.
Have you checked, or do you understand correct prop/motor mounting height? That is critical with a pontoon. You said the boat was new to you, propping is simple in concept but can get expensive if guessing.
Is your prop damaged?
Ass-um-ing the prop is good, the motor is good, and not being there, the motor may be mounted too high. I'd check that first.
I switched from my higher pitched props to my 3-16x12 because my rpm was 5300-5400 when pulling teens and tubes. Too low for me.

there is a plastic "ring" that fits inside the gearcase in front of the prop on most mercs., including mine. It is to prevent ventilation from exhaust gases. They get broken, forgotten, missing, check yours.

 

[joegibbstruck]

what is the diameter of your pontoons? Makes a big difference.

I have a 2006 , 24' pontoon, 25" diameter toons and a 2021 Mercury 115 hp CT, purchased new.
By myself I get 26 mph, 5800+ rpm @WOT. Both a Merc 4-14x14 and a 3-16x13 props give these numbers.
A merc. 3-16x12 prop gets me over 6000 rpm and about 24 mph but I used that prop to pull two tubes with 5 thin teenagers and 4 on board which kept my rpms around 5600+ and about 21+ mph. What I wanted.
When pulling a load, I wanted my motor's rpm in the upper range of the 5000-6000 rpm operating range. ( don't know yours).
Your boat is 2' shorter and 10 more horses. Your performance should be better than mine, unless your toons are smaller.
Have you or do you understand correct prop/motor mounting height? That is critical with a pontoon. You said the boat was new to you, propping is simple in concept but can get expensive if guessing.
Is your prop damaged?
Ass-um-ing the prop is good, the motor is good, and not being there, the motor may be mounted too high. I'd check that first.
I switched from my higher pitched props to my 3-16x12 because my rpm was 5300-5400 when pulling teens and tubes. Too low for me.

there is a plastic "ring" that fits inside the gearcase in front of the prop on most mercs., including mine. It is to prevent ventilation from exhaust gases. They get broken, forgotten, missing, check yours.

24" toons, I also thought the motor may be too high, but it sits as low as it will go on the transom and it is the factory mounted motor for the boat. operating range is 4750-5250 and 5450rpm is the rev limiter, the aluminum prop has small knicks on the end of a couple of blades, but I don't think it would be enough to hurt the performance this much. Which is why I'm thinking the 15p is too much pitch, your 3-blade prop is a 2" less pitch and 2" larger diameter than mine Which would give you a larger amount of traction than what I have I'm at I don't know what your gear ratio is... but I plug a 2.0 like mine then you have ~25% slip vs my 49% There is also not a plastic ring Infront of the prop on my motor. I'm guessing I need to go larger diameter and less pitch, which would theoretically bring my slip down and hopefully my speed up a bit.